An exhaust-gas aftertreatment arrangement for an internal combustion engine in a vehicle typically comprises a catalytic converter for reducing harmful emissions. A catalytic converter in general comprises a canned and coated catalytic converter substrate in flow communication with inlet and outlet passages. It is positioned on the exhaust side of the internal combustion engine of the vehicle in order to treat exhaust gas emissions from the engine.
During cold start and warming-up of the engine, the catalytic converter is typically not sufficiently heated for optimum performance and the exhaust gas emissions may therefore pass through the catalytic converter without catalytic conversion thereof. To improve the heating properties, the catalytic converter is often positioned as close as possible to the exhaust ports. To accelerate heating, it is also possible to heat the catalytic converter electrically or to temporarily control combustion such that the temperature of the exhaust gas heat flow is increased.
Furthermore, a low pressure drop of an exhaust-gas aftertreatment system is desirable to improve performance and to reduce energy losses. A known method of reducing the pressure drop is to arrange two or more catalytic converters in parallel to increase the flow capacity of the exhaust-gas aftertreatment arrangement. A reduced pressure may also be achieved by increasing the size of the catalytic converter.
However, increasing the size of the catalytic converter, or arranging several catalytic converters in parallel, also increases the total thermal mass of the catalytic converters thereby exacerbating the above discussed problem relating to cold starts and certain operating conditions.
Accordingly, there is a need for an improved exhaust-gas aftertreatment arrangement allowing the pressure drop to be reduced, particularly at high engine loads, while reducing emissions due to catalytic converters operating below a preferred operating temperature.